(a) Technical Field
The present invention relates to a thin film transistor and a method of forming the thin film transistor, and more particularly, to an oxide semiconductor thin film transistor with improved reliability and a method of forming the thin film transistor.
(b) Discussion of the Related Art
A liquid crystal display includes a first substrate including a pixel electrode, a second substrate including a common electrode, and a liquid crystal layer interposed between the first substrate and the second substrate and having dielectric anisotropy.
An electric field is formed between the pixel electrode and the common electrode, and the intensity of the electric field is controlled to change the arrangement of liquid crystal molecules of the liquid crystal layer.
Accordingly, the retardation of light passing through the liquid crystal molecule is controlled, thereby displaying desired images.
A thin film transistor is used as a switching element for the liquid crystal display.
The thin film transistor (TFT) has a gate electrode, a drain electrode, a source electrode, and an active layer.
When the gate electrode is applied with a voltage of more than a predetermined value, the active layer is activated so that a current flows between the drain electrode and the source electrode.
As a material forming the active layer of the thin film transistor (TFT), amorphous silicon (a-Si) or polysilicon (p-Si) may be used.
Recently, the tendency toward large size and highly miniaturized TFT-LCDs has accelerated, and a next generation active layer for realization thereof is required.
Particularly, if high resolution and a driving technique are applied to the large size display, it is necessary to reduce wire resistance and parasitic capacitance and to improve the characteristics of the thin film transistor with regard to the driving of the panel.
For the improved performance of the thin film transistor, a micro-crystalline Si TFT or an oxide semiconductor is being actively researched as the next generation candidate.
However, the thin film transistor having the micro-crystalline Si has a channel region with low electron mobility, and deposition equipment must be developed.
The oxide semiconductor has electron mobility that is higher by several tens of times than the amorphous silicon thin film transistor such that the charging capacity of the pixel is good. Further, the oxide semiconductor allows a driving circuit to be integrated on the substrate. Because of the merits, the oxide semiconductor is being developed.
The thin film transistor including the oxide semiconductor may be electrically influenced by its structure and the processing conditions in the dry etching or wet etching process.
Accordingly, research related to element structure and a reliable process is required.